This invention is directed generally to material distribution apparatus and more particularly to a novel and improved control system for a mobile material distribution apparatus such as a vehicular spreader.
Mobile material distribution apparatus such as vehicular spreaders for distributing "solid" or granular material and vehicular sprayers for distributing liquid products are known in the art. In such material distribution apparatus, it is generally desired to control the rate, usually by weight, of material distribution per unit area. Accordingly, as the vehicle travels along the ground at a given speed, the rate of distribution of material will be dependent upon both the vehicle speed and the rate at which material is delivered to distribution apparatus of the vehicular sprayer or spreader.
The rate of distribution achieved will further vary in accordance with the relative density of the product being distributed, as well as the width of the spread or spray pattern achieved by the spray nozzle or nozzles or by the "solid" or granular spreading apparatus utilized. In this regard, it will be appreciated that the control systems and variables to be considered in both liquid and solid material application are analogous. Liquid distribution may include such applications as the spraying of liquid fertilizers, weed control products or the like upon a field. Similarly, "solid" or granular material spreading may find application in the distribution of granular fertilizer or similar materials over a field as well as in the distribution of ice control chemicals in granular form upon a road or highway.
While the present invention is not so limited, the description will be facilitated by specific reference to a solid or granular material distribution apparatus or spreader. Generally speaking, control systems for such material distribution apparatus have heretofore controlled the rate of delivery of material to a spinner or similar material distribution device in accordance with the speed of the vehicle to achieve a desired spread or application rate. Such control systems take into account not only the rate of material delivery to this distribution device and the speed of the vehicle, but also the density of material being distributed and the width of the spread pattern. The foregoing variables are utilized in achieving suitable control of the rate of delivery of material to the distribution device, usually in weight per unit time. Such control assures distribution of material to a field or highway at the desired weight per unit area.
There is room for improvement in such systems, however. For example, it is generally desirable in such systems to avoid excessive "hunting" in the operation of the control system in achieving corrections of the material delivery rate. In this regard, it is generally desirable to maintain a relatively smooth operation of mechanical control members in achieving any corrections or variations in the material delivery rate. This in turn maintains the distribution or application rate substantially constant at the desired rate.
In this regard, a conveyor is generally utilized to deliver material from a hopper or other supply of material to one or more distribution devices, such as "spinners" commonly utilized in the spreading of granular material. This conveyor is provided with a variable speed motor, which is often hydraulically controlled. The hydraulic control system may further be provided with a movable member or flow control valve which controls the flow of hydraulic fluid to the conveyor drive motor and hence the speed thereof. This hydraulic control valve may be manually adjusted. However, it is the practice in such control systems to further provide an electric motor for controlling the position of the hydraulic valve remotely, for example, from the operator's station of the vehicle.
Prior art automatic control systems have generally devised various means for effecting automatic control of the position of the valve in accordance with the desired application rate of material. The aim is to achieve a substantially constant, desired application rate irrespective of changes in the speed of the vehicle. It will be recognized, however, that the hydraulic valve and associated drive motor have some inertia or resistance which prevents reliable response thereof to control signals below a certain threshold level. Hence, relatively fine adjustments thereof are often difficult to obtain.
Moreover, the hydraulic, electrical and mechanical components of such a system will experience various tolerances or variations from their nominal operating characteristics. These variations should be taken into account in achieving accurate control of material distribution or application rate.